1. Field of the Invention
The present invention relates to an assembly structure of power semiconductor device that is to be implemented for power transistors, thyristors, diode modules, etc.
2. Description of Prior Art
A conventional assembly structure of power semiconductor device is shown in FIG. 4. Reference numeral 1 is a power circuit comprising a heat radiating aluminum insulated substrate 1a that has a power semiconductor element 1b mounted thereon; 2 is a control circuit comprising a printed-wiring board 2a that has circuit components 2b mounted thereon; 3 is a flexible substrate interconnecting the power circuit 1 and the control circuit 2; 4 is a resin case in which the power circuit 1 and the control circuit 2 are incorporated; 5 is the lid of the case; 6 and 7 are power terminals of a frame type and control terminals of a fast pin type, respectively, that are drawn out of the case 4 via drawing pockets formed on its peripheral edge; 8 is a molding resin (epoxy resin) with which the power terminals 6 and the control terminals 7 are secured in the case 1; and 9 is a gel of sealing resin (silicone gel) with which the case is filled.
The semiconductor device having the structure shown in FIG. 4 is assembled by the following procedure. First, the power element 1b and the power terminals 6 are mounted and soldered onto the aluminum insulated substrate 1a. Further, the flexible substrate 3 for establishing interconnection with the control circuit 2, as well as the control terminals 7 are mounted and soldered onto the aluminum insulated substrate 1a. Subsequently, the case 4 is mounted and adhered onto the aluminum insulated substrate 1a and, thereafter, the sealing resin 9 is injected into the case 4 through the opening in the top, followed by filing the terminal drawing areas with the molding resin 8, which is then cured. Thereafter, the lid 5 is placed on top of the case 4, terminal nuts 10 are fitted in the case 4 and, finally, the drawing ends of the power terminals 6 are bent in such a way that they are placed over and in registry with the nuts 10.
The conventional assembly structure above described have the following problems with respect to the process of assembly, the quality of the final product, and its cost.
(1) It is necessary in the assembly process to retain the power and control terminals in predetermined attitudes when they are soldered. At subsequent stages, the molding resin 8 and the sealing resin 9 are injected and cured in the case 4 in separate steps and, furthermore, the terminal nuts 10 must be inserted and the power terminals 6 bent, increasing the total number of steps involved in the assembly process while reducing its operating efficiency.
(2) Since the power terminals 6 and the control terminals 7 are to be secured in the case 4 by means of the molding resin 8, the drawout positions of the terminals will be offset on account of the shrinkage that occurs upon resin curing, whereby the positional precision of the terminals drops. Consequently, defects will occur as exemplified by difficulty in the process of bending the leads from the power terminals 6 (the holes in the terminals will not be in registry with the positions of the terminal nuts) and by the failure of the control terminals 7 of a fast pin type to align correctly in a row, causing difficulty in the subsequent handling (connecting leads to an external circuit).
(3). The flexible substrate 3 interconnecting the power circuit 1 and the control circuit 2 is expensive and, furthermore, a sophisticated assembling technique is required in connecting the flexible substrate to each circuit; hence, the final product will become too costly to be used commercially.